The invention relates to a procedure for hardening at least one surface of a wall of a component and a device specially suited for executing this procedure.
The problem when hardening surfaces on walls of components is that the objective is to achieve the desired quality of hardening on the one hand, while preventing the wall in question from losing the toughness required for the respective application of the component. Therefore, it is necessary to prevent the wall from becoming heated through while heating the surfaces to be hardened.
This can be accomplished during the use of inductors, which heat the surfaces to be hardened by inducing an electromagnetic field, by setting the penetration depth of the field generated by the inductor according to the required depth of hardening in the area of the surface to be hardened. However, this process presumes that a sufficient wall thickness is present in the area of the surface to be hardened. Otherwise, the wall cannot be prevented from heating through, and hence hardened through due to heat migration.
Therefore, when hardening of relatively thin-walled components, a change has been made in practice to cooling with liquid the wall lying opposite the side of the wall having the surfaces to be hardened, By suitably metering the cooling liquid stream, the penetration depth of the heat generated in the wall by the inductor, and hence the depth of hardening in the area of the surface to be hardened, can be set even in thinwalled components.
Special requirements are placed on the hardening of surfaces on the walls of a component with respect to front-drive motor vehicles, in which the drive torque is transferred via sliders, which sit moveably in a so called xe2x80x9ctripodxe2x80x9d. Such a tripod is shaped like a bowl, and exhibits several supporting and running surfaces angled relative to each other and extending in a longitudinal direction, axially parallel to the longitudinal axis of the tripod. The sliders arc guided on these supporting and running surfaces. At the same time, the supporting surfaces absorb the torque transferred by the sliders. To be able to withstand this load, the supporting and running surfaces must be hardened. At the same time, the toughness of the wall material must be retained, despite the hardening of the surfaces, so that the tripod can withstand the alternating torque loads while driving the vehicle.
The object of the invention is to provide a procedure of the kind described above, which enables a hardening of at least one surface adapted to the respective requirements, even on the walls of complexly shaped components with a small wall thickness. In addition, a device suitable for executing this procedure is to be specified.
This object is achieved in terms of the procedure for hardening at least one surface of a wall of a component by virtue of the fact that the surface to be hardened is inductively heated with at least one inductor, that a liquid is filled in a gap present between the surface to be hardened and the inductor while heating the surface to be hardened, that the side of the wall lying opposite the side of the wall provided with the surfaces to be hardened is applied with liquid as the surface to be hardened is heated, and that at least one liquid jet is aimed at a zone of the wall adjacent to the surface to be hardened, which is to be prevented from being heated by the inductor.
According to the invention, not only is the side of the wall lying opposite the side of the wall provided with the surface to be hardened wetted with cooling liquid, but liquid is additionally aimed at the zone of the side of the wall that borders the surface to be hardened, and is not to be encompassed by hardening. The additional liquid jet transports away the heat that arises in the zone to be excluded from heating due to the influence of the induced electromagnetic field. In this way, not only the penetration depth of the hardening zone can be specifically predetermined in the area of the surfaces to be hardened, also its surface expansion can.
Therefore, the procedure according to the invention makes it possible to form precisely delineated hardening zones, whose expansion and depth are adapted to the respective structural requirements and loads of the component provided with the hardened surfaces. For example, a progression of the edge of the hardened surfaces established precisely based on the orientation and progression of the liquid jets can be generated by virtue of the fact that the liquid jets are each aimed at the wall provided with the surface to be hardened in sections or in a specific sequence, and transport away the heat arising there. In this way, for example, a sufficiently soft wall material can be provided at precisely the locations where deformation is to be executed after hardening the wall surfaces for structural or assembly-related reasons.
At the same time, because the gap between the inductor and surface to be hardened is filled with liquid, the field generated by the inductor penetrates into the wall to be heated in a uniform fashion. In this way, a homogeneous processing result can be ensured, even though streams of cooling liquid are continuously supplied while heating the surfaces that would otherwise disrupt the uniformity of heating.
The procedure according to the invention is particularly suited for hardening surfaces on walls of those components in which the wall envelops an interior space, and the surfaces to be hardened are arranged on the side of the wall allocated to the interior space. The uniform filling of the gap between the inductor and surface to be hardened can be ensured in a particularly simple manner in these types of components. Additionally in structural members designed like this, several surfaces can be hardened simultaneously. This also applies in particular in cases where at least two adjacent surfaces angled relative to one another are each hardened at the same time, as is the case with respect to the tripods described at the outset, for example.
One particularly intensive, short-term inductive heating of the surface to be hardened limited to a specific, narrowly delineated surface and depth can be achieved by generating the electromagnetic field at high frequency. In this way, the inductive heating of the surfaces to be hardened can advantageously take place at a frequency of up to 80 kHz, for example.
A device particularly well-suited for executing the procedure according to the invention is equipped with an inductor for heating the surface to be hardened, a liquid feed line, through which liquid gets into the gap between the inductor and the surface to be hardened, a first sprayer, which aims at least one liquid jet at the side of the wall lying opposite the side of the wall provided with the surface to be hardened, and with at least one additional sprayer, which aims the liquid jet at the zone of the wall to be precluded from hardening.
In this case, it is particularly beneficial if the sprayer whose jet is aimed at the zone to be precluded from hardening be carried by the inductor. This type of design of the device according to the invention can be realized with a low technical outlay, and yields a compact shape for the required structural members. The latter is always of particular importance in cases where only a little space is available inside the device for the inductor and sprayers.